Satellite stabilizer



1962 I R. E. ROBERSON ETAL 3,048,108

SATELLITE STABILIZER Filed Sept. '7, 1956 2 Sheets-Sheet 1 t l0 l3' RATEGYRO FIG. 2 INVENTOR. A ROBERT E. ROBERSON BENJAMIN P. MARTIN BY KENNETHH. ROGERS ATTOR NEY Aug. 7, 1962 Filed Sept. 7, 1956 FIG. 4

R. E. ROBERSON ETAL 3,048,108

SATELLITE STABILIZER 2 SheetsSheet 2 INVENTORS ROBERT E. ROBERSONBENJAMIN P. MARTIN BY KENNETH H. ROGERS ATTORNEY United States PatentOfi ice 3,048,108 SATELLITE STABILIZER Robert E. Roberson, Fullerton,Kenneth H. Rogers, Long Beach, and Benjamin P. Martin, Pacoima, Calif.,assignors ,to North American Aviation, Inc.

Filed Sept. 7, 1956, Ser. No. 610,878 2 Claims. (Cl. 102-50) Thisinvention relates to the yaw attitude stabilization of any bodytravelling in an orbit, for example, a satellite vehicle. Moreparticularly, it pertains to a gyroscopic device which, by properorientation within a satellite vehicle, adds to the stabilizationthereof.

Satellite vehicles can be devised to be inherently stable in theirattitudes. A pitch and roll stabilization can be obtained by verticalelongation of the vehicle frame. However, enhancement of yawstabilization by elongation in the roll direction is quite limitedbecause of the usual requirement of circular cross-sections of thesatellite normal to its for-ward axis during ascent through theatmosphere into the orbit.

The purpose of this invention is to enhance yaw stability when inherentvertical stability exists. The invention consists of a rotating wheel,mounted so that its spin axis lies along a positive pitch axis of thevehicle. The wheel may be run at a constant speed, or, in order tocompensate for external pitch-producing torques, the wheel may beoperated at varying speeds.

The novelty of this invention is that the device provides a stabilizingtorque in yaw (and to some extent in roll) without the sensing ofattitude and without the need for determining or computing the vehiclemotion and without the expenditure of energy, except that required toovercome motor losses in the flywheel, or gyroscope, which are typicalexample of a suitable rotating wheel.

At least a part of the function of the flywheel described above can beobtained by the rotating parts already existing in the vehicle. Forexample, motors, generators, and other rotating equipment, whose angularmomentum vector is constant may be aligned parallel to the vehicle pitchaxis and serve as the device of the invention.

It is therefore an object of this invention to provide an improvedstabilizing element for a satellite vehicle.

It is another object of this invention to provide a gyroscopicstabilizer for a satellite vehicle.

It is still another object of this invention to provide yaw and rollstabilization with a minimum of equipment.

A still further object of this invention is to provide an inherentlystable satellite vehicle.

Other objects of invention will become apparent from the followingdescription taken in connection with the accompanying drawings, in whichFIG. 1 illustrates a satellite vehicle in an orbital path;

FIG. 2 is a vertical cross section of the vehicle structure;

FIG. 3 is a horizontal cross section of the vehicle; and

FIG. 4 illustrates a satellite vehicle and its x, y and z axes, togetherwith its roll and yaw angles and 0 Referring now to FIG. 1, a satellitevehicle 1 in an orbital path 2 moves around earth 3. The localgeocentric vertical 4 is drawn from the vehicle to the earths center ofgravity. If the least principal moment of inertia of vehicle 1 liesabout line 4, the gravity gradient naturally tends to align vehicle 1 asshown. The vehicle thus rises through the atmosphere nose first and thenmoves broadside in its orbital path.

FIG. 2 illustrates a satellite vehicle, showing its frame incross-section. Theconcept of the invention comprises rigidly mounting aspinning wheel 6 with respect to the vehicle frame. The plane of thevertical axis 4 and the orbit path 2 is perpendicular to the spin axisof the Patented Aug. 7, 1962 Cd wheel. Pitch axis 9 is parallel to thespin axis 5 of the flywheel 6 and may be further located by reference toFIG. 1.

In essence, the plane of rotation of flywheel 6, if initially aligned tothe plane of the orbit 2, will act to remain in the plane of orbit 2 andmaintain satellite vehicle 1 stabilized to overcome yaw-producingtorques. Further, the tendency of flywheel 6 to align its plane ofrotation parallel to the orbital plane provides a torque to stabilizethe vehicle in roll as well as yaw.

The enhancement of yaw and roll stability can be realized by any wheelwhich rotates at constant angular velocity relative to the vehicleframe. In the case of disturbing torques acting about the yaw and rollaxes, the gyro functions as a direct stabilizer. Thus, understeady-state conditions, a disturbing torque about the yaw axis 4results in angular precession of the gyro (and the vehicle structureassociated therewith) about the roll axis of the vehicle which issubstantially the orbital path 2 (see for reference FIG. 2). Suchtorque, of course, results in a precession velocity about the roll axis(substantially lying along the line indicating orbital path 2) dependingupon the gyro rotor moment of inertia, and the gyro rotor spin velocity.A similar disturbing torque about the roll axis which substantially liesalong orbital path 2 would result in a similar angular precession of thegyroscope about yaw axis 4. Such precessional affect is well-known tothose skilled in the art of gyroscopes. In addition, the same wheel maybe used to compensate for pitch perturbation torques if its speed issuitably varied about some steady-state value. The precessionalcharacteristics of a gyroscope, of course, can not stabilize about thethird axis (parallel to pitch axis 9); however, the rotor may be usedmerely as an inertial reaction torque device, and its acceleration ordeceleration controlled to obtain stabilization about the pitch axis 9.As the rotor of the gyroscope is increased in speed an opposing reactionforce is created against the stator portion of the motor, according to'Newtons laws of motion, in an opposite direction. Therefore, when anypitch is detected by rate gyro 13 the speed of the rotating machinerymay be increased or reduced in order to counteract such pitch motion. Inthis case, switch 17 is thrown to connect in a rate gyro 10 whosesensitive axis 13 is mounted to detect any angular velocity about axis9, the pitch axis, to drive the amplifier 11 which in turn drives theflywheel motor 12, or motors, to cause the wheel to increase or decreasespeed, as the case may be, so as to oppose the pitching motion detectedby the rate gyro. This is in addition to the constant speed controller16 which causes the flywheel to have a constant speed in the absence ofany rate gyro signal.

FIG. 3 is a view taken on line 3-3 of FIG. 2, showing the flywheel inplan view. The pitch axis 9, the vertical axis 4, and the path 2 areillustrated in their orientation with respect to the flywheel. Struts,such as 14 and 15, fixedly mount the wheel bearings 7 with respect tothe body.

As mentioned previously, the effect of the flywheel may be obtained fromthe rotating machinery already contained within the vehicle, such asmotors, generators, gears, pulleys, etc., whose axes of rotation arealigned as illustrated in FIGS. 2 and 3. It is not essential, therefore,that all rotating means be located at the center of the vehicle. It isonly essential that the net external angular momentum be perpendicularto the orbital plane. It will be noted that no attitude sensing withrespect to earth is required in this system. If compensation obtained bythe rate gyro 10 is not desired, pitch stabiliza- 0 tion torques may beobtained solely by other means and flywheel 6 is rotated at a constantspeed by means of input 16, which may, for example, be simply an inputfrom a D.-C. source; or it may involve feedback from a tachometer orpotentiometer driven by the flywheel motor.

FIG. 4 illustrates the satellite in its x, y, z coordinate system. Ascan be seen, 0 is the angle of roll (about roll axis x), and 0 is theangle of yaw (about yaw axis z).

The attribute of the pitch flywheel which causes it to rotate in theplane of the orbit is observed in the dynamical equations of motion ofthe vehicle. For the simple case of a circular orbit in an inertiallyfixed plane, the roll angle, 0 measured about an axis lyingsubstantially along orbital path 2, measured from and perpendicular tothe orbital plane, and the yaw angle, 0 measured about axis 4 from andperpendicular to the orbital plane, satisfy the coupled equations asfollows:

are the principal moments of inertia of the satellite vehicle about itsyaw (Vertical), pitch and roll (forward) axes, respectively. The x axisof the satellite vehicle is the forward axis of the vehicle as itproceeds along its orbital path broadside (assuming the vehicle has noyaw angle nor pitch angle). The z axis is the vertical axis of thesatellite, (assuming it has no pitch angle nor roll angle). The y axisis the lateral axis of the vehicle as it proceeds along its orbital pathbroadside (assuming the vehicle has no yaw angle nor roll angle). The x,y and z axes are orthogonal with respect to each other and are the roll,pitch and yaw axes respectively of the vehicle.

o is the orbital frequency,

H is the spin angular momentum of the flywheel as seen relative to thevehicle frame,

L and L are the roll and yaw torques acting on the vehicle.

From Equation 2 it can be seen that the term Hw fl corresponds to a yawrestoring torque with a spring constant of H0 in excess of any springconstant lwhich may have been present originally. This yaw restoringtorque is added by the device of th invention.

Two other functions are apparent, the term Hw fl may introduce yawstability into the system Where it was not previously present, and theterm Hw fi in Equation 1 implies additional roll stability necessarilyaccompanies increased yaw stability.

Although some yaw stability can be gained by elongation of the vehiclealong axis 2, there is a limit, as explained previously, to which thiscan be done and still maintain the practical missile shape for ascent.The device of this invention implements the yaw stabilization withoutrequiring undue elongation of this dimension.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

We claim:

1. Means for stabilizing a satellite vehicle wherein said vehicle orbitsaround a celestial body in an orbital plane at a speed suificient tocreate a centrifugal force substantially equal to the gravitational pullbetween said vehicle and said celestial body, said stabilizing meansincluding a rotatable wheel attached to said body, the plane of rotationof said wheel being oriented with respect to said body so as to beparallel with said orbital plane of said body, means for controlling thespeed of said rotating wheel according to the pitch agular velocity ofsaid body.

2. Means for stabilizing a satellite vehicle wherein said vehicle orbitsaround a celestial body in an orbital plane at a speed sufiicient tocreate a centrifugal force substantially equal to the gravitational pullbetween said vehicle and said celestial body, said means including agyroscope comprising a rotating wheel, a motor for rotating said wheel,a bearing mounting said rotating wheel fixedly with respect to saidvehicle except about the rotatable axis of said wheel, a rate gyroscopeattached to said vehicle, said motor for rotating said wheel being atleast response to the output of said rate gyroscope.

DunajelT June 19, 1923 Turner May 29, 1951 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,048, 108 August 7, 1962 Robert E.Roberson et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should readascorrected below.

Column 3 lines 15 to 23, the equations (1) and (2) should appear asshown below instead of as in the patent:

where 1 I and 1 column 4, line 2, for "th" read the line 30, for"agular" read angular same column 4, lines 41 and 42, for "response"read responsive Signed and sealed this 12th day of May 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

